This invention relates to a display device for digitally displaying the receiving frequency of a radio receiver or the like.
In a conventional display device of this type, the receiving frequency per se of a receiver or a local oscillation frequency corresponding to the receiving frequency is counted by a frequency counter, so that the receiving frequency is displayed on a display unit according to the count result of the frequency counter. The display device is so designed that a numerical value is displayed by suitable display elements such as light emission diodes in the display unit. For instance, in the case of an FM receiver whose receiving frequency range is from 76.0 MHz to 90 MHz, the receiving frequency of the receiver being tuned, such as 82.5 MHz or 90.0 MHz or the frequency of a broadcasting station when the receiver is completely tuned thereto, is displayed on the display unit. In this display device, the frequency displayed on the display unit is varied during the tuning operation of the receiver. For instance, if the receiving frequency is changed from 82.5 MHz to 90.0 MHz, the frequency display is changed 73 times as "82.6", "82.7", . . . and "90.0". In this case, the following difficulty occurs: A numerical value displayed on the display unit is changed according to the rate of the tuning operation, and therefore it is difficult to read the displayed numerical value instantaneously; that is, it is difficult to find the tuning point instantaneously. The degree of the difficulty is increased as the receiving frequency is greatly changed as in the case where the receiver is tuned from the frequency of one broadcasting station to the frequency of another broadcasting station which is greatly different from the former. This is due to one of the characteristics of the eyes of a person; that is, the eyes of the operator tend to watch a changeable numerical value especially. For instance, in the above-described tuning operation, the 10th MHz digit and the first MHz digit are changed slowly, but the 100th KHz digit is changed quickly. Therefore, the operator watches the variation of the 100th KHz digit rather than the 10th MHz digit and the first MHz digit. As a result, it is difficult to instantaneously recognize the entire numerical value. Thus, the conventional display device suffers from the drawback that the tuning operation cannot be achieved in a short time.